Carbon Structures with Hollow Internal Cavity as Charge Storage Materials to Achieve High Energy Density

Abstract

Hollow porous carbon spheres (HPCS) have been synthesized by using spherical silica nanoparticles (S–SiO 2 ) as templates. S–SiO 2 nanoparticles have been coated first with the polymer of phloroglucinol/1,4-phenylenediamine/formaldehyde (PPF), followed by a second layer of SiO2, and again with PPF as the third layer. After each step of coating, the sample has been pyrolyzed under nitrogen and S–SiO 2 has been removed to obtain HPCS-I, HPCS-II, and HPCS-III, from the first, second, and third coated samples, respectively. The synthetic strategy relies on the use of a hard template to create void spherical cores and space confinement to develop shells of the hollow spheres. All of the materials show a uniform spherical morphology with a hollow inner core generated by the removal of the SiO2 template. The samples have been characterized by thermal analysis, powder X-ray diffraction, nitrogen adsorption/desorption studies, electron microscopy, and X-ray photoelectron spectroscopy. Among the samples, the structural formation of HPCS-II is found to be superior and it is also manifested in its electrochemical properties. While all of the samples exhibit near-rectangular cyclic voltammograms, the specific capacitance of HPCS-II is found to be the highest. Galvanostatic charge/discharge (GCD) studies also support the observation, and the specific capacitance is found to be 592 F·g–1 at a current density of 1 A·g–1, which is retained at 444 F·g–1 even at a very high current density of 100 A·g–1. The major contribution toward such electrochemical behavior is believed to arise from electrical double-layer capacitance (EDLC). HPCS-II is found to be highly stable, retaining 100% of its capacitance value at least up to 5000 GCD cycles. The power density of HPCS-II is nearly thrice the power target value projected by the Partnership for a New Generation of Vehicles (PNGV), and it shows an outstanding energy density value.

Ni Single Atom Decorated Porous Hollow Carbon Nanosphere‐Based Electrodes for High Performance Symmetric Solid‐State Supercapacitors

“…In this study, Ni atom incorporated N‐doped hollow carbon nanospheres have been synthesized by simultaneous reduction of Ni 2+ to Ni and condensation of phloroglucinol‐formaldehyde to their polymeric resin in the presence of NH 3 . Here NH 3 acts as the base, [34] source of nitrogen as well as the morphology‐controlling catalyst to produce spherical particles in ethanolic medium with the cationic surfactant CTAB and tri‐block co‐polymer Pluronic P123 as the porogens and co‐stabilizers (Scheme 1). [35] Spherical monodisperse particles of phloroglucinol‐formaldehyde polymer have been synthesized first by an extended Stöber's method [36] and then a layer of silica is coated over the polymer nanospheres by employing TEOS in the presence of NH 3 and CTAB.…”

“…The graphitic-N centres can improve the electron transfer rate effectively whereas the pyrrolic-N and pyridinic-N sites provide extra pseudocapacitance by increasing the ion diffusion rate through numerous contactable defects and active sites thereby providing abundant open pathways. [14,34] The pyrrole-N species is the primary binding site responsible for stabilizing the Ni single atoms because of its strong coordination affinity. [31] The deconvoluted spectra for O 1s core level of the samples (Figures 3c, S10c and S11c) show binding energy peaks at ca.…”

“…The specific energy densities (E) in Wh kg À 1 and specific power densities (P) in W kg À 1 were calculated from equations (v) and (vi) given below, respectively. [34] E ¼ 1 2…”

B/P-Codoped Porous Carbon Electrode for Supercapacitors with Ultrahigh Energy Density

“…The specific capacitances of the various samples have been calculated from the cyclic voltammetric studies using the following equation: C s = ∫ v normali v normalf I false( v false) d v ( v normalf − v normali ) · S · m where C s is the specific capacitance in F/g, “ m ” is the mass of the active electrode material in g, “ S ” is the scan rate in V/s, “( v f – v i )” is the working potential window in V, and “ ∫ v normali v normalf I false( v false) d v ” is the area under the corresponding cyclic voltammogram (CV).…”

“…Supercapacitor electrodes based on N-doped carbon materials have been widely reported in the literature . The materials show good basicity to interact with acidic electrolytes, resulting in high gravimetric capacitance, good rate capability, and excellent stability in charge/discharge cycles . Inclusion of O atoms is invariably associated with any carbonization process, and hence there is a certain content of O atoms in the carbon samples depending on the carbonization conditions.…”